Fysbis Backdoor Preferred by Pawn Storm Group to Target Linux

Researchers at Palo Alto Networks have performed an in-depth analysis of Fysbis, the preferred Linux malware used by the Pawn Storm threat group. The simple, yet efficient tool is proving to be effective because Linux security in general is still a maturing area, the experts say.

Pawn Storm is a well-known cyber espionage group believed to have ties to the Russian government. Also known as Sofacy, APT28 and Sednit, the group has been around since 2007, targeting government, military, and defense organizations around the world, as well as various Eastern European governments.

Over the years, Pawn Storm has used a multitude of tools for its attack operations, such as zero-day exploits in Flash, Java or Microsoft Office, spear-phishing, and website compromise. Their tools target multiple operating systems, including Windows, OS X, Linux, and iOS, but Fysbis appears to be their malware of choice when it comes to infiltrating Linux systems.

The tool, a modular Linux Trojan / backdoor that implements plug-in and controller modules as distinct classes, is not sophisticated, Palo Alto’s Bryan Lee and Rob Downs explain in a blog post. The malware includes 32-bit and 64-bit versions of Executable and Linking Format (ELF) binaries and can install itself onto a system with and without root privileges.

The researchers note that the lack of sophistication displayed by this malware suggests that Advanced Persistent Threat (APT) actors don’t require advanced means to reach their objectives. They also note that, while these actors do own advanced malware and zero-day exploits, they often keep them in reserve and use the smallest amount of resources needed to meet their goals.

The Fysbis analysis revealed that the malware checks the Linux version during installation, and runs a series of shell commands to establish persistency. Recently, the group behind the malicious program improved their obfuscation technique, to ensure that the installation information is no longer leaked in the clear, as had been the case prior.

By looking at several malware samples, researchers discovered that, while some did beacon to domains previously known to be used for command and control (C&C) by the Pawn Storm group, others called back to new domains. The newly found C&C domain mozilla-plugins[.]com wasn’t previously associated with the group, nor was the IP address it resolves to.

Palo Alto Networks believes that the domain and IP are associated to a newer campaign, although the malware samples show similarities at the code level and in terms of shared behavior. What is clear, however, is that while other adversaries seem hesitant to change their infrastructure, Pawn Storm did invest in additional resources to do so, although some Fysbis samples displayed the same type of behavior.

According to Palo Alto Networks researchers, Fysbis has contributed to the success of associated attacks by the Pawn Storm / Sofacy group mainly because Linux security is missing key elements. They also note that expertise in the Linux platform is highly sought after across all industries, as the platform remains largely unknown even to enterprise IT specialists.

Linux is used across a broad variety of environments, including homes, cloud, and the majority of Internet-facing web and application servers, while also being the foundation of the Android mobile platform. However, it also poses a high risk to organizations’ security posture because Linux malware and vulnerabilities do exist and are in use by advanced adversaries, while detection and prevention is not prevalent at this time.